An electrophotographic image forming apparatus that includes a process of transferring a toner image formed on a surface of an image bearing member to a transfer material such as paper has been well-known. A color image forming apparatus generally employs a configuration in which multiple photosensitive members are lined up, toner images are sequentially formed by the respective photosensitive members, and the toner images are transferred to a transfer material directly or via an intermediate transfer member.
Recent diversification of printer demands has been accompanied by a rise in request for no-margin print in the color image forming apparatus in particular. There has conventionally been known a method, in which a transfer material slightly larger than an image is used and margins thereof after printing are cut. To simplify the cutting work, the necessity of so-called no-margin print of printing an image on an entire surface of the transfer material without forming any margins on the edges of the transfer material beforehand has increased.
For an ink-jet image forming apparatus, an apparatus with a no-margin print function has been brought to the market. For example, Japanese Patent Application Laid-Open No. H10-337886 discloses the technology.
In an attempt to realize an electrophotographic full-color image forming apparatus that supports no-margin print, there arise the following technical problems.
During an image forming operation, on the transfer material after a toner image transfer process, toner may be transferred not only to the surface of the transfer material but also to at least one of edge surfaces of the transfer material located at four sides surrounding the transfer material.
In this case, when the transfer material enters a fixing device, the toner of the edge portions of the transfer material may not be fixed to paper at a fixing nip to cause a fixing failure. As a result, an offset phenomenon occurs on surfaces of a fixing film and a pressure roller. In the case where this offset occurs, when the offset toner is adhered again to the top surface or the back surface of the transfer material, a toner smear occurs in the transfer material, resulting in an image failure.